CHIRAL FLUCTUATIONS AND STRUCTURES

Chiral molecules form a number of non-chiral structures,the simplest b eing an isotropic fluid phase. In a mesophase of achiral molecules the fluctuations will on an average be achiral as well: left-handed twist s and right-handed twists will occur with the same probability. In a s ystem composed of chiral molecules, however, the fluctuations will be biased in one direction or the other, and there will be optical effect s such as a non-zero fluctuation induced rotary power in addition to t he molecular rotary power of the individual molecules. We discuss this effect in a number of contexts, including lyotropic lamellar phases. When the tendency to twist is strong enough or the line energy of havi ng an exposed edge is small enough,a new, defect riddled ground state of a lyotropic lamella, akin to the Renn-Lubensky twist-grain-boundary phase of thermotropic smectics, can occur.